Applied voltage control device for sensor

Abstract

An applied voltage control device is used for a sensor, in which a direct current corresponding to an oxygen amount flows when a DC voltage is applied to the sensor, and an alternating current corresponding to a sensor impedance flows when an AC voltage is applied to the sensor. The applied voltage control device includes: a filtering unit that sets a cutoff frequency of the AC voltage applied to the sensor variable.

What is claimed is: 
     
       1. An applied voltage control device for a sensor, in which a direct current corresponding to an oxygen amount flows when a DC voltage is applied to the sensor, and an alternating current corresponding to a sensor impedance flows when an AC voltage is applied to the sensor, the applied voltage control device comprising:
 a heater that heats the sensor to control the temperature of the sensor to be a predetermined set temperature; and 
 a filtering unit configured to switch between different cut-off frequencies to selectively set a cut-off frequency of the AC voltage applied to the sensor to be variable, wherein 
 the filtering unit is configured to set the cut-off frequency to be variable based on element temperature related information related to an element temperature of the sensor, the element temperature related information includes a heater current when the heater heats the sensor, and 
 the filtering unit is configured to selectively set the cut-off frequency to be high in response to a determination that the heater current is large and selectively set the cut-off frequency to be low in response to a determination that the heater current is small. 
 
     
     
       2. The applied voltage control device according to  claim 1 , wherein:
 the filtering unit sets the cut-off frequency to be high when the element temperature is low, and sets the cut-off frequency to be low when the element temperature is high, based on element temperature related information. 
 
     
     
       3. An applied voltage control device for a sensor, in which a direct current corresponding to an oxygen amount flows when a DC voltage is applied to the sensor, and an alternating current corresponding to a sensor impedance flows when an AC voltage is applied to the sensor, the applied voltage control device comprising:
 a heater that heats the sensor to control the temperature of the sensor to be a predetermined set temperature; and 
 a filtering unit configured to switch between different cut-off frequencies to selectively set a cut-off frequency of the AC voltage applied to the sensor to be variable, wherein 
 the filtering unit is configured to set the cut-off frequency to be variable based on element temperature related information related to an element temperature of the sensor, the element temperature related information includes a heater current when the heater heats the sensor, and 
 the filtering unit is configured to selectively set the cut-off frequency to be high in response to a determination that the heater current is small and selectively set the cut-off frequency to be low in response to a determination that the heater current is large. 
 
     
     
       4. An applied voltage control device for a sensor, in which a direct current corresponding to an oxygen amount flows when a DC voltage is applied to the sensor, and an alternating current corresponding to a sensor impedance flows when an AC voltage is applied to the sensor, the applied voltage control device comprising:
 a heater that heats the sensor to control the temperature of the sensor to be a predetermined set temperature; and 
 a filtering unit configured to switch between different cut-off frequencies to selectively set a cut-off frequency of the AC voltage applied to the sensor to be variable, wherein 
 the filtering unit is configured to set the cut-off frequency to be variable based on element temperature related information related to an element temperature of the sensor, the element temperature related information includes a sensor heating power that is an amount of power consumption when the heater heats the sensor, and 
 the filtering unit is configured to selectively set the cut-off frequency to be high in response to a determination that the sensor heating power is small and selectively set the cut-off frequency to be low in response to a determination that the sensor heating power is large. 
 
     
     
       5. An applied voltage control device for a sensor, in which a direct current corresponding to an oxygen amount flows when a DC voltage is applied to the sensor, and an alternating current corresponding to a sensor impedance flows when an AC voltage is applied to the sensor, the applied voltage control device comprising:
 a heater that heats the sensor to control the temperature of the sensor to be a predetermined set temperature; and 
 a filtering unit configured to switch between different cut-off frequencies to selectively set a cut-off frequency of the AC voltage applied to the sensor to be variable, wherein 
 the filtering unit is configured to set the cut-off frequency to be variable based on element temperature related information related to an element temperature of the sensor, the element temperature related information includes a sensor heating time that is an amount of elapsed time when the heater heats the sensor, and 
 the filtering unit is configured to selectively set the cut-off frequency to be high in response to a determination that the sensor heating time is short, and selectively set the cut-off frequency to be low in response to a determination that the sensor heating time is long. 
 
     
     
       6. The applied voltage control device according to  claim 3 , wherein:
 the filtering unit sets the cut-off frequency to be high when the element temperature is low, and sets the cut-off frequency to be low when the element temperature is high, based on element temperature related information. 
 
     
     
       7. The applied voltage control device according to  claim 4 , wherein:
 the filtering unit sets the cut-off frequency to be high when the element temperature is low, and sets the cut-off frequency to be low when the element temperature is high, based on element temperature related information. 
 
     
     
       8. The applied voltage control device according to  claim 5 , wherein:
 the filtering unit sets the cut-off frequency to be high when the element temperature is low, and sets the cut-off frequency to be low when the element temperature is high, based on element temperature related information. 
 
     
     
       9. The applied voltage control device according to  claim 4 , further comprising
 a microcomputer configured to output a command signal to the filtering unit to control the filtering unit to selectively set the cut-off frequency in response to a determination regarding the element temperature related information. 
 
     
     
       10. The applied voltage control device according to  claim 5 , further comprising
 a microcomputer configured to output a command signal to the filtering unit to control the filtering unit to selectively set the cut-off frequency in response to a determination regarding the element temperature related information. 
 
     
     
       11. The applied voltage control device according to  claim 4 , wherein
 the microcomputer is configured to output a command signal to the filtering unit to control the filtering unit to selectively set the cut-off frequency to switch between different detection states that each have a predetermined variation in the sensor impedance. 
 
     
     
       12. The applied voltage control device according to  claim 5 , wherein
 the microcomputer is configured to output a command signal to the filtering unit to control the filtering unit to selectively set the cut-off frequency to switch between different detection states that each have a predetermined variation in the sensor impedance.